Field of the Invention
The invention relates to a monitoring system for monitoring the window panes of an interior having a plurality of window panes and lateral and/or upper and/or lower walls surrounding the window panes, by means of a microphone configuration, in which the microphone configuration in each case can receive the sonic vibrations typically produced in the ultrasonic range above 100 kHz when a pane is broken, for example for monitoring a motor vehicle interior for intruders.
The invention was in fact developed for the monitoring of a motor vehicle interior, and more specifically for the monitoring of the window panes of a motor vehicle for pane breakage. The invention is not only suitable for monitoring the interior of a motor vehicle or other vehicles by monitoring the window panes, but it is also suitable for monitoring the window panes of fixed property, for example the window panes of warehouses.
The monitoring system initially defined above is known, for example, from British Patent No. 1 402 530, and in particular from FIG. 1 thereof, together with the associated description. In that system the structure-borne sonic vibrations produced in the monitored window panes are monitored above 100 kHz and up to several hundred kHz, by fastening one corresponding piezoceramic sensor on each of the window panes to be monitored. In other words, numerous correspondingly suitable microphone configurations are fastened for each interior, as described, for example, on page 2, left column, last paragraph of the British patent.
In that frequency range, structure-borne sonic vibrations in particular propagate through the window panes very well, whereas sonic vibrations can propagate in the air only with considerable damping in such an ultrasonic range. Accordingly, that known monitoring system is very insensitive to disturbances caused by air-borne sonic vibrations in such a frequency range if the air-borne sound comes from sound sources outside the space.
In fact, the invention also uses sound frequencies above 100 kHz for interior monitoring, as a result of which the monitoring system according to the invention is likewise very insensitive to air-borne sound in that frequency range if the disturbing source of the air-borne sound is outside the monitored space. However, the invention does not use the measurement of the structure-borne sound propagating in the window panes that is produced when a pane is broken. The invention thus also avoids the disadvantage of such prior art wherein a high outlay is required, namely in each case one sensor for each window pane to be monitored together with the wiring and the associated evaluation means therefor, and the frequently additional disadvantage that it is sometimes difficult, if not impossible, to detect as pane breakage a relatively small breakage of the window pane which is remote from the point at which the sensor touches the window pane.
In addition, it is known from U.S. Pat. No. 4,665,379 to monitor the various window panes of a motor vehicle interior by means of a single microphone configuration, wherein the microphone configuration is fastened in the motor vehicle interior or to its walls measuring the air-borne sonic vibrations in the frequency range from 5 kHz to around 8 kHz. The air-borne vibrations propagate in the air in the interior in that frequency range virtually without damping. Although the outlay for microphones and wiring is correspondingly low with such a monitoring system, the outlay for eliminating the disturbances caused by sources of air-borne sound outside the motor vehicle interior is correspondingly increased.
Furthermore, for monitoring an interior, it is known from German Published, Non-Prosecuted Application DE 35 04 552 A1 to measure the air-borne sound by means of a microphone configuration at two ultrasonic frequencies, namely at 40 kHz and at 50 kHz or, in accordance with the figure in that reference, to measure a relatively narrow band of one of the two frequencies by means of a bandpass filter on one hand, and the entire frequency range from ZERO up to the other of the two ultrasonic frequencies by means of a low-pass filter on the other hand. Up to such frequencies, the air namely still transmits the respective vibrations quite well. However, in that case, the sound sources radiating outside the space can then still represent considerable interference since not all of their sound is reflected outward at the outer surface of the space.
In addition, series of in-house experiments have shown that crafty intruders can easily damp the sonic vibrations produced in the window panes, primarily in the frequency range up to 50 kHz, but also well above it. However, the object of the invention was to provide a system with which the intruder could no longer successfully employ such damping measures. It was not the intention of the invention to rely on such a measurement of the ultrasonic vibrations.
It is well-known to the person skilled in the art how to form the directional characteristic of a microphone configuration, even for ultrasound, in accordance with a particular special requirement. For example, reference is made to:
U.S. Pat. No. 2,833,999, PA1 U.S. Pat. No. 3,833,825, PA1 U.S. Pat. No. 4,395,652, PA1 U.S. Pat. No. 4,597,099, PA1 Published European Application No. 0 037 620 A1, PA1 Published European Application No. 0 075 302 A1, PA1 Published European Application No. 0 308 899 A2, PA1 French Patent No. 2 293 844, and PA1 German Published, Prosecuted Application DE-AS 28 55 143.
The invention thus relates to the monitoring of an interior, wherein, as in the case of the monitoring system described in British Patent No. 1 402 530, the sonic vibrations triggered by a pane breakage are measured above 100 kHz, such sonic vibrations being propagated very well in many materials such as in glass, but only poorly in the air.
It is accordingly an object of the invention to provide a monitoring system for monitoring the window panes of a space, for example a motor vehicle interior, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type.
The invention achieves the object:
of being able to simultaneously monitor numerous window panes of the interior for pane breakage in the frequency range above 100 kHz with approximately an equally high degree of reliability, with a particularly low outlay, especially with a single microphone configuration, even if the number of window panes it has to monitor is very high and some of the window panes to be monitored are in the vicinity of the sensor and others are very far away from it,
of being able to simultaneously avoid by and large interfering influences due to foreign noises from the environment by the employment of these high frequencies, and also
of being able to by and large avoid the erroneous non-detection of pane breakages since, as in-house experiments on motor vehicle window panes have shown, an intentional pane breakage is still all too frequently undetected if only the frequencies below 100 kHz are utilized as soon as an intruder damps the ability of the breaking window pane to vibrate by some means or other, which is an aspect that also precludes the measurement of the structure-borne sound then propagating in the window pane.
With the foregoing and other objects in view there is provided, in accordance with the invention, in an interior having a plurality of window panes and lateral and/or upper and/or lower walls surrounding the window panes, a monitoring system for monitoring the window panes, for instance in a motor vehicle interior, comprising a single microphone configuration fastened in the interior and/or to at least one of the walls of the interior, for receiving sonic vibrations typically produced in the ultrasonic range above 100 kHz when a pane is broken, the single microphone configuration monitoring essentially only the sonic vibrations transmitted by air in the interior with considerable damping in the ultrasonic range above 100 kHz, and the microphone configuration having a directional characteristic being matched to the geometry of the monitored interior and allowing the reception of the sonic vibrations received in the case of a breakage of remote pane areas to be monitored, at least as a rule with high sensitivity similar to the sonic vibrations being received in the case of a breakage of proximate pane areas to be monitored.
The invention is moreover suitable for additionally employing the sensor for other interior monitoring methods, which possibly even utilize quite a different frequency range of the received vibrations: the invention namely allows the microphone configuration to be additionally used as, for example, a receiving element of an acoustic radar system, instead of just as an element for detecting pane breakage. The invention then additionally allows the detection of suspicious movements in the space, to be precise, and likewise with a particularly low outlay, and even with a low outlay for the microphone configuration.
With the invention it is above all possible to secure all the glass areas of a motor vehicle with the single microphone configuration, as will be explained below. Therefore, in comparison to the known monitoring systems, through the use of the invention the ultrasonic frequencies above 100 kHz transmitted by the air in the interior are evaluated. In this case, with the invention the distance between the microphone configuration and the glass areas to be monitored may even be several meters.
In accordance with another feature of the invention, the interior is an interior of a motor vehicle to be monitored having a longitudinal axis, and the microphone configuration is attached approximately above the longitudinal axis of the motor vehicle and has a more or less heart-shaped directional characteristic. This feature allows the employment in a motor vehicle of a mirror-symmetrical directional characteristic which is particularly easy to produce, that is to say, for example, a microphone configuration having a directional characteristic forming two slightly overlapping lobes in a manner which is particularly easy to produce.
In accordance with a further feature of the invention, the interior is an interior of a motor vehicle having a windshield with an upper edge in the vicinity of which the microphone configuration is attached. In this way, a particularly favorable solution for a motor vehicle is offered, with which it is readily possible to avoid obstacles, for example headrests, between the sensor and the window panes to be monitored. In addition, it is much more difficult for an intruder to destroy the window pane and the sensor simultaneously than if the sensor were attached to the lower edge of the window pane. Moreover, the sensor can then even be built into the base of the interior rear-view mirror, or else into interior illumination means attached at that location, and therefore permit a particularly unobtrusive solution with a particularly attractive construction.
In accordance with an added feature of the invention, the interior is an interior of a motor vehicle having a rear window with an upper edge in the vicinity of which the microphone configuration is attached. This feature allows another favorable solution for a motor vehicle to be offered, with which the sensor can also be attached quite unobtrusively in the roof covering at that location and with which it is likewise readily possible to avoid obstacles, for example headrests, between the sensor and the window panes to be monitored. In addition it is much more difficult for an intruder to destroy the window pane and the sensor simultaneously than if the sensor were attached to the lower edge of the window pane.
In accordance with an additional feature of the invention, the microphone configuration at least from time to time is a microphone configuration of an acoustic radar system in a suitable frequency range, being able to deviate from a frequency range used for monitoring pane breakage.
In accordance with a concomitant feature of the invention, the radar system additionally utilizes the Doppler effect.
These features allow the microphone configuration to be utilized as a receiving element of an acoustic radar too.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a monitoring system for monitoring the window panes of a space, for example a motor vehicle interior, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.